Thermostatically controlled electric switch



NOV. 17, 1936. A J, s BRIGGS 2,061,346

THERHOSTATICALLY CONTROLLED ELECTRIC SWITCH Filed Aug. 26, 1955 James fiezlekicl' Yb-eel" Br gg:

Patented Nov. '11, 1936 ELECTRIC James Frederick Street Whangarei,

New

Zealand Application August 26, 1925, Serial No. 38,001

In New Zealand September 4, 19:4

, 5 Claims. (01. 200-140) This invention has been devised with the ob .ject ofproviding an improved combination and arrangement of parts to form a thermostatical- 1y controlled switch for governing the electric 5 supply current to various forms of appliances adapted to be heated by such current. The invention devised provides for the current being so controlled and governed that the closing of the switch, to complete the circuit, is efiected o mechanically, and its opening to break the circuit, is effected automatically upon the temperature conditions surrounding the switch reaching a predetermined degree.

The invention has special application in its 5 features of construction to an ordinary electric iron, for the purpose of preventing the over heating thereof, and the resultant danger of fire should the iron be left unattended with the. current supply on.

vice for use in the control of the temperature thereof.

In describing the invention and in its illustration in the accompanying drawing, it is described 25 and illustrated as being fitted in an ordinary electric iron but it is desired to emphasize that in giving eiiect to the invention, the various details concerned with the formation and disposal of the parts may be varied from those shown 30 without departing from the spirit of the inven- Figure 3 is a rear end elevation thereof, the

coverin this case also being in section. 40 Figure 4 is a detail sketch view that will hereinafter be more fully referred to.

The 'iron is made in any of the known and approved wa'ys having a sole plate l and cover H and the ordinary heating element shown by dot- 45 ted lines at l2 in Figure 2,-adapted tube connected to the terminal pins ii. In this invention the connection between one of the pins l3 and one end of the heating element has the control means interposed therein to make and break the 50 circuit in the manner provided for. The said control means may conveniently be mountedonacarryinsplate thatisflxedto the sole plate II by suitable fastenings it, which came it to extend above the element, but other 55 meansfcrcarryingthesepartsmaybedevised It, however, also has applica- 20 tion to any other form of electrically heated deto suit each circumstance of the inventions application.

The control means comprise two contact pieces l6 which are fixed side by, side upon an insulating block I! upon the plate It near one corner of its back end. From each of these pieces a leaf i8 extends inward, and in parallel alignment with thatof the other piece. Acting in conjunction with these contacts is a bridging piece l9 that is carried upon an insulator block 20 aflixed to 10 the free end of a thermostatic bow 2|. The other end of this how is made fast to the plate l4 so that in the expansion and contraction of the bow its free end recedes from and approaches the contacts IS. The said bridging piece has formed therewith two parallel leaves IS and these are so disposed that when the bow end is moved to close on to the contacts i6 one leaf 19* passes underneath a leaf i8 of one contact while the other leaf Ii! passes across the top of the 20 leaf l8 of the other contact, thereby to effect a more definite electric connection between them and also allowing for the definite breakingof the contacts when the bow moves out. The connection between one of the iron terminals I3 5 and the corresponding end of the heating element is made through the pieces l6 which are interposed in the connection, so that when the bridge i9 is in engagement therewith, the circuit is complete and when out of engagement, the circuit is broken.

In this invention the said thermostatic how 2! is made of a mercury containing tube formed on the well known Bourdon tube principle but sealed by an electric or like welding method to enclose the mercury.

The invention embodies means for acting in conjunction with the bow 2| whereby it may be moved to its circuit closing position and engaged and held until the heat acting thereon reaches a 4 predetermined degree, when, under the opening tension of the bow, it will release itself from the retaining means and spring open. These means consist in an arm 22 that is fixed to project out from the free end of the bow 2|, and a block 23 secured to the plate I and having a cam edge 24 over which the end of the arm 22 is caused to slide in the opening and closing movements of the bow, and which cam edge has a notch 25 situated at its inner end into which the end of the am is adapted to spring when the arm read es that point in the closing of the bow. The end of the arm preferably is fitted with an agate or 11kg knob 20 to ensure of its free movement along the camedge. Whenthereiorethebowismovedin,

the arm end, by slipping into the notch 2!, will be engaged and held'to prevent the bow opening, but this engagement is of such a nature that it will give and release the bow when the opening tension of the bow becomes strong enough under the expansive action of the heat of the iron thereon.

The closing of the switch by moving the bow end inward is designed to be efiected manually by the operation of a key 2| inserted through a key aperture in the iron cover II to fit over a pin 29 suitably placed on the plate It, The ward of this key is adapted when the key is turned, to engage the arm 22 upon the bow end and force the bow in until the arm end engages the notch 26, and then to pass free. The key is preferably made as shown in the detail drawing Figure 4 so that the part 30 of the ward 6118 8 8 the edge of the arm 22 is formed of lead or other metal fusible at low temperatures, so that should thekey jamb in its engagement with the arm in closing the switch and remain in its jambed position, the heating of the iron will melt this portion of the ward and thereby allow the arm and bow to spring out when the predetermined temperature is reached. In all ordinary use of the iron it is proposed to remove the key from the iron after it has performed its switch closing function, it be-. ing necessary then .to re-insert it should the tion of the cam edge 24 may be varied in relation to the line of movement of the arm 22. For this purpose it may be fixed to the plate I l, as shown in Figure l, by means of a screw 32 passing through it near one edge, and a screw 33 passing through a curved slot 34 near the other edge. By loosening the screws the block may be turned on the screw 32 as a pivot to the angle required. Other ways of providing for this regulation may however be employed.

It will be readily apparent that the appliances described may be adapted'i'or use in connection with other electric heating circuits to provide for similar effects in respect of the control of the current thereto and particularly to prevent any over heating.

1. Thermostatic switch control means for electric heating circuits, comprising the combination with a pair of contact pieces interposed in the electric supply circuit of a thermostatic bow fixed at one end and supplied with an insulated bridging piece upon its free end and so positioned as to cause such bridging piece, on the contraction of the bow, to engage and bridge the said pair of contacts and, on the expansion of the bow. to move away from such engagement, and detent means adapted to engage and hold the free end of the bow when it is moved into the contact bridging position but to release it when its opening tension increases to a predetermined extent, said detent means for the thermostatic bow-embodying an arm projecting from the free end of the bow, and a fixed block formed with a cam edge along which the end of the arm slides in the contracting and expanding movements of the bow andwhichcamedgeismade withanotchinto whichthe armendspringswhenthebowhas reached the circuit closing position.

2. Thermostatic switch control means for electric heating circuits, comprising the combination withapairofcontactpiecesinterposedinthe electric supply circuit of a thermostatic bow fixed at one end and supplied with an insulated bridging piece upon its free end and so positioned as to cause such bridging piece, on the contraction of the bow, to engage and bridge the said pair of contacts and, on the expansion of the bow. to move away from such engagement, and detent means adapted to engage and hold the free end of the bow when it is moved into the contact bri in position but to release it when its opening tension increases to a predetermined extent, said detent means for the thermostatic bow embodying an arm projecting from the free end oi the bow, and a fixed block formed with a edge along which the end of the arm slides in the contracting and expanding movements the bow and which cam edge is made with a notch into which the arm end springs when the bow has reached the circuit closing position, said cam block being so fixed to its base that the angle of inclination of the cam edge, in relation to the line of movement of the arm end, may be varied.

3. Thermostatic switch control means for electric heating circuits comprising a base plate, a pair of contact blocks aflixed to the base plate and having spring fingers projecting therefrom. a thermostatic bow formed by a mercury tube sealed by a welding method, having one end fastened to the base plate and the other end arranged adjacent to the said spring fingers, a bridging piece carried upon the free end of the bow and insulated therefrom and adapted to engage and to free the said spring fingers upon the contraction and expansion of the how, a block secured upon the base plate adjacent to the free end of the bow and made with a cam edge extending along it and having a notch near one end thereof, and an arm attached to the free end of the bow the end of which slides along such cam edge in the contracting and expanding movements of the how.

4. Thermostatic switch control means for electric heating circuits according to claim 3 in which the said base plate is provided with a key swivelling pin disposed adjacent to the arm upon the said thermostatic bow, substantially as and for the purpose specified.

5. Thermostatic switch control means for electric heating circuits, comprising the combination with a pair of contact pieces interposed in the electric supply circuit and each formed with a spring iinger extending laterally therefrom, of a thermostatic bow fixed at one end, a bridging piece secured upon the free end of the bow and formed with a pair of laterally extending spring fingers so positioned as to cause them to engage respectively with the spring fingers of the said contact pieces, with respective underlapping and overlapping engagement, on the contraction of the bow, and to break such engagement when the bow expands, and detent means adapted to engage and hold the bow when it moves into the JAMES FREDERICK STREET BRIGGS. 

